Came home from work last night to find that the heat had stopped working on the coldest day of the season. (20's all day, 1/4" of freezing rain/sleet fell)

Unit is an outdoor Trane furnace/AC "all in one", natural gas. It was installed in 2006, and had never been serviced.

Luckily, the one HVAC guy that answered his phone happened to be a few miles away, he came out at around 8PM, despite the bad road conditions.

The gas valve seemed to be bad, so he swapped in a new one. No improvement, gas wasn't getting to the valve. He then got a torch and warmed up the regulator, which happens to next to the unit, exposed to the weather, and the black plastic cap had popped off (months ago) and was sitting nearby. That got gas flowing to the valve, but it still didn't light. Turns out he put the valve in backwards, so he reinstalled. (obviously he'd had a long day)

Now the gas would light, but wouldn't stay lit. He checked the flame sensor, and it had white residue on it, so he cleaned it off...still nothing. This particular unit has two...burners (?), one has the flame sensor and the other has the ignitor. he said the channel between the two was dirty, so the flame from the lit burner wouldn't get over to light the other.

After all this, everything seemed to work. House was warm until I went to bed, but I woke up to a cold house.

It's still cold outside, roads are still icy, etc.

The only thing I felt comfortable doing myself was to cycle the ignition. I took a hair dryer to the regulator, and tried again. Furnace has been on for about an hour now, hasn't turned off since the house is still cold.

I'm left wondering what the original problem was...the valve, or the regulator, or a combination of several things? The problem doesn't seem to be fixed, should I go back to the original repair guy, or find someone else? What should I request that he do? Do regulators "go bad"? Should I do something to keep it warm, maybe heat tape or...? Could there be moisture trapped within the regulator?